CN112325979B - Dynamic closed-loop control multichannel capacitive oil mass sensor signal conditioning system and method - Google Patents
Dynamic closed-loop control multichannel capacitive oil mass sensor signal conditioning system and method Download PDFInfo
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- 230000003750 conditioning effect Effects 0.000 title claims abstract description 37
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- 230000000087 stabilizing effect Effects 0.000 claims abstract description 49
- 238000005259 measurement Methods 0.000 claims abstract description 31
- 238000005070 sampling Methods 0.000 claims abstract description 24
- 238000001914 filtration Methods 0.000 claims abstract description 18
- 239000003990 capacitor Substances 0.000 claims description 86
- 230000005284 excitation Effects 0.000 claims description 45
- 238000006243 chemical reaction Methods 0.000 claims description 18
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- 125000004122 cyclic group Chemical group 0.000 abstract description 2
- 239000003921 oil Substances 0.000 description 50
- 238000011105 stabilization Methods 0.000 description 9
- 230000006641 stabilisation Effects 0.000 description 8
- 238000010586 diagram Methods 0.000 description 4
- 239000000295 fuel oil Substances 0.000 description 4
- 239000007788 liquid Substances 0.000 description 4
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- 239000000446 fuel Substances 0.000 description 3
- 239000010687 lubricating oil Substances 0.000 description 2
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- 230000007274 generation of a signal involved in cell-cell signaling Effects 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
- G01F23/22—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
- G01F23/26—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of capacity or inductance of capacitors or inductors arising from the presence of liquid or fluent solid material in the electric or electromagnetic fields
- G01F23/263—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of capacity or inductance of capacitors or inductors arising from the presence of liquid or fluent solid material in the electric or electromagnetic fields by measuring variations in capacitance of capacitors
- G01F23/266—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of capacity or inductance of capacitors or inductors arising from the presence of liquid or fluent solid material in the electric or electromagnetic fields by measuring variations in capacitance of capacitors measuring circuits therefor
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- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
- G05D9/00—Level control, e.g. controlling quantity of material stored in vessel
- G05D9/12—Level control, e.g. controlling quantity of material stored in vessel characterised by the use of electric means
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Abstract
The invention belongs to the technical field of monitoring and control, and provides a signal conditioning system and a method for a dynamic closed-loop control multichannel capacitance oil mass sensor, aiming at the problems of poor precision and stability and long circuit stabilizing time of a traditional signal conditioning circuit, wherein the system mainly comprises an idle load stabilizing circuit, a sample hold and filter circuit and the like, and the method comprises the following steps: the dynamic voltage signal is utilized to carry out closed-loop control, fast and stable sampling and holding, filtering circuit and no-load stabilizing circuit, so that the stabilizing time of the capacitance acquisition conditioning circuit is shortened, and the cyclic conditioning acquisition of the multi-measurement-channel capacitance signal can be completed; meanwhile, the added no-load stabilizing circuit and the fast stabilizing sample hold and filter circuit do not influence the acquisition precision and the anti-interference capability; the invention has high measurement accuracy, strong anti-interference and easy realization, and can effectively reduce the multi-path capacitance conditioning cost. The method is suitable for industrial embedded monitoring and aviation electronic products.
Description
Technical Field
The invention belongs to the technical field of monitoring and control, and is mainly used for monitoring aviation fuel quantity and lubricating oil quantity. In particular to a signal conditioning system and a method for a dynamic closed-loop control multichannel capacitance oil quantity sensor, which are used for monitoring the fuel oil level through online real-time multiple measuring channels and providing accurate fuel oil quantity information for a control and monitoring system.
Background
In the state monitoring and control of the aero-engine, the fuel oil liquid level is monitored, accurate fuel oil quantity information and overrun warning information are provided for an engine control system and an aircraft system, correct control and flight safety of the engine are related, and the method has important significance for the aero-engine field. The accurate collection of aviation fuel quantity and lubricating oil quantity generally adopts a capacitive sensor, can conveniently convert liquid level quantity into electric capacity, and realizes monitoring and control of liquid level.
At present, a capacitive oil quantity sensor is mostly adopted in an aeroengine, and after receiving an alternating current excitation signal with a certain amplitude and a certain frequency, the capacitive oil quantity sensor outputs a micro capacitance signal of a pF level. The oil quantity of the whole engine can be calculated through a special circuit and a signal conditioning method. The traditional signal conditioning circuit has the defects of poor general precision and stability and long circuit stability time; as in chinese patent CN108613715A, an "acquisition system for aviation fuel quantity sensor based on ac ratio method" is disclosed, its main principle is that the exciting ac voltage signal is converted into charge signal through the capacitor to be acquired, and then is converted into dc voltage signal through the charge amplifier and the precision rectifying and filtering circuit, where the dc voltage signal and the capacitance value have a definite relationship, and the measured capacitance value can be calculated, but because of the weak nature of the charge signal and the open loop test principle of the system, the anti-interference capability is poor, the effective value conditioning circuit has long stabilizing time, resulting in low signal refresh rate and other disadvantages; in addition, as in chinese patent CN108225495A, a "capacitive liquid level sensor on-line measurement method and system thereof" is disclosed, the main principle is that a variable frequency triangular wave oscillating circuit is formed by collected capacitors, a definite relationship exists between signal frequency and capacitance value, and the measured capacitance value can be calculated, but the antijamming capability is poor due to the influence of open loop characteristic and parasitic capacitance of the system, especially for self-excited oscillating circuit, the self-excited frequency error is affected by multiple factors such as resistance precision and voltage precision of voltage stabilizing tube, so the whole circuit has longer stabilizing time and poorer precision.
Disclosure of Invention
Aiming at the problems of poor precision and stability and long circuit stability of the traditional signal conditioning circuit, the invention provides a signal conditioning system and a method for a dynamic closed-loop control multichannel capacitive oil mass sensor.
In order to achieve the above object, the technical scheme of the present invention is as follows:
A dynamic closed-loop control multichannel capacitance oil mass sensor signal conditioning system is characterized in that: the device comprises an excitation circuit, a driver, a protection circuit, n no-load stabilizing circuits, a multi-measurement channel acquisition controller, a current conversion voltage circuit, an integration amplifying circuit, a sampling hold and filtering circuit, an A/D acquisition unit, a CPU and a voltage feedback circuit; wherein n is a positive integer greater than or equal to 1;
The excitation circuit, the driver and the protection circuit are electrically connected in sequence;
the capacitance oil quantity sensor Cx to be measured is positioned between the protection circuit and the n no-load stabilizing circuits;
the n no-load stabilizing circuits, the multi-measurement channel acquisition controller, the current conversion voltage circuit, the integration amplifying circuit, the sampling hold and filtering circuit and the A/D acquisition unit are electrically connected with the CPU in sequence;
the input end of the voltage feedback circuit is connected with the output end of the integrating amplifying circuit, and the output end of the voltage feedback circuit is connected with the output end of the multi-measurement-channel acquisition controller;
The excitation circuit is used for outputting alternating current square wave excitation signals with equal positive and negative amplitudes; the driver is used for amplifying the alternating square wave excitation signal; the protection circuit is used for protecting static electricity and thunder and lightning; the alternating-current square wave excitation signal is converted into an alternating-current signal through a cable and a capacitance oil quantity sensor Cx to be detected in sequence;
The input ends of the n no-load stabilizing circuits are respectively connected with the output ends of the capacitance oil quantity sensors Cx to be measured of each measuring channel and are used for stabilizing alternating current signals flowing through the capacitance oil quantity sensors Cx to be measured of the measuring channels in no-load state; the empty state measuring channel is an unconnected measuring channel;
The input end of the multi-measurement channel acquisition controller is respectively connected with the output end of each no-load stabilizing circuit and is used for selecting and connecting each measurement channel;
making a difference between the alternating current flowing through the capacitance quantity sensor Cx to be detected and the current flowing through the reference capacitor C ref;
The current conversion voltage circuit is used for converting the difference value between the alternating current flowing through the capacitance oil quantity sensor Cx to be detected and the current flowing through the reference capacitor C ref into a voltage signal; the integrating amplifying circuit is used for amplifying the voltage signal and outputting amplified alternating current dynamic voltage; the voltage feedback circuit is used for feeding back the amplified alternating current dynamic voltage to the reference capacitor C ref to form a new reference capacitor current value, so that dynamic balance of the Cx current of the capacitor oil mass sensor to be tested and the reference capacitor current is realized; the sampling hold and filter circuit is used for sampling and filtering the alternating current dynamic voltage signal and outputting a direct current stable voltage signal V out_p; the A/D acquisition unit is used for converting V out_p into a digital signal, the CPU is used for acquiring the V out_p digital signal, and the digital signal is converted into a corresponding capacitance oil quantity sensor Cx value to be measured through the following formula:
V out_p= 2×Cx×Vexe_p/ Cref, wherein: v out_p units are V; c x is the capacitance to be measured of the oil quantity sensor, and the unit is pF; v exe_p is the peak voltage of the alternating current excitation signal, and the unit is V; c ref is the reference capacitance in pF.
Further, the no-load stabilizing circuit comprises a resistor R1 and a grounding capacitor C1, one end of the resistor R1 is connected with the output end of a measuring channel of the capacitance oil quantity sensor to be measured, and the other end of the resistor R1 is connected with one end of the grounding capacitor C1 and the input end of the multi-measuring channel acquisition controller; the other end of the capacitance to ground C1 is grounded.
Further, the sample-hold and filter circuit includes SPST3ON, resistor R2, capacitor C2, follower and two diodes;
One end of the SPST3ON is connected with the output end of the integrating amplifying circuit, the other end of the SPST3ON is connected with one end of a resistor R2, the other end of the resistor R2 is grounded through a capacitor C2 and is simultaneously connected with the forward input end of a follower, and the output end of the follower is connected with the reverse input end and the input end of the A/D acquisition unit; two diodes are connected in parallel at two ends of the resistor R2, wherein the anode of one diode is connected with one end of the resistor R2, and the cathode of the other diode is connected with one end of the resistor R2.
Further, the voltage feedback circuit includes a third reference voltage source, an SPST2ON switch, an SPST2OFF switch, and a reference capacitor C ref; one end of the SPST2ON switch is connected with the output end of the integrating amplifying circuit, and the other end of the SPST2ON switch is connected with one end of the reference capacitor C ref; the output end of the third reference voltage source is connected with one end of the SPST2OFF switch, and the other end of the SPST2OFF switch is connected with one end of the reference capacitor C ref; the other end of the reference capacitor C ref is connected with the output end of the multi-measurement channel acquisition controller.
Further, the current-converting voltage circuit includes a capacitor C3, a resistor R4, a capacitor C4, SPST4ON and SPST4OFF;
One end of the capacitor C3 is connected with the output end of the multi-measurement channel acquisition controller and the output end of the voltage feedback circuit, the other end of the capacitor C3 is connected with one end of the resistor R3 and one end of the resistor R4, the other end of the resistor R3 is connected with one end of the SPST4ON switch, and the other end of the SPST4ON switch is grounded; the other end of the resistor R4 is connected with one end of an SPST4OFF switch, and the other end of the SPST4OFF switch is grounded through a capacitor C4 and is simultaneously connected with the input end of the integrating amplifying circuit.
Further, the excitation circuit comprises a first reference voltage source, a second reference voltage source, an SPST1ON switch and an SPST1OFF switch; the output end of the first reference voltage source is connected with one end of the SPST1ON switch, the output end of the second reference voltage source is connected with one end of the SPST1OFF switch, and the other ends of the SPST1ON switch and the SPST1OFF switch are connected with the positive input end of the driver.
Further, the duty cycle of the alternating square wave excitation signal with equal positive and negative amplitudes is 50%.
The invention also provides a conditioning method based on the dynamic closed-loop control multichannel capacitance oil quantity sensor signal conditioning system, which is characterized by comprising the following steps of:
step 1: the processor controls the excitation circuit to output alternating-current square wave excitation signals with equal positive and negative amplitudes, and the alternating-current square wave excitation signals are converted into alternating-current signals through the driver, the protection circuit, the cable and the capacitance oil quantity sensor Cx to be tested in sequence;
Step 2: an alternating current signal passing through a capacitance oil quantity sensor Cx to be detected enters an idle load stabilizing circuit;
Step 2.1: when the multi-measurement channel acquisition controller does not select the measurement channel to be connected, an alternating current of the measured capacitor and a ground capacitor of the no-load stabilizing circuit form a current loop, so that voltage stabilization (alternating current stabilization) at two ends of the ground capacitor is realized, no current loop in the no-load process is avoided, namely, before the multi-measurement channel is connected by the multi-selector, the current flowing through the Cx of the capacitance oil quantity sensor to be measured is in a stable state;
Step 2.2: when the multi-path selector selects the measuring channel to be connected, an alternating current signal of the measuring channel corresponding to the capacitance oil quantity sensor Cx to be measured enters a current conversion voltage circuit; the stabilized current flowing through the capacitance oil quantity sensor Cx to be measured enters a new stable state again according to the load change;
Step 3: the current conversion voltage circuit converts the difference value between the alternating current flowing through the capacitance oil quantity sensor Cx to be detected and the current flowing through the reference capacitor C ref into a voltage signal, and the voltage signal passes through the integrating and amplifying circuit to output amplified alternating current dynamic voltage; the amplified alternating current dynamic voltage is fed back to a reference capacitor C ref through a voltage feedback circuit to form a new reference capacitor current value, so that dynamic balance of Cx current of the capacitor oil mass sensor to be detected and reference capacitor current is realized;
Step4: the alternating current dynamic voltage output and amplified by the integrating and amplifying circuit passes through a sampling hold and filtering circuit, and the sampling hold and filtering circuit samples and filters signals and outputs a direct current stable voltage signal V out_p; the sample hold voltage is in direct proportion to the measured capacitance;
Step 5: the A/D acquisition unit converts V out_p into a digital signal, the CPU acquires the V out_p digital signal, and the digital signal is converted into a corresponding Cx value of the capacitance oil quantity sensor to be detected through the following formula:
V out_p= 2×Cx×Vexe_p/ Cref, wherein: v out_p units are V; c x is the capacitance to be measured of the oil quantity sensor, and the unit is pF; v exe_p is the peak voltage of the alternating current excitation signal, and the unit is V; c ref is the reference capacitance in pF.
Further, the step 1 specifically comprises the following steps: outputting direct current signals with equal amplitude and opposite positive and negative values by using a first reference voltage source and a second reference voltage source; the SPST1ON switch and the SPST1OFF switch are controlled by square wave signals, so that direct current signals with opposite positive and negative are respectively changed into alternating current square wave excitation signals through the SPST1ON switch, the SPST1OFF switch and the driver; the square wave peak voltage V exe_p is determined by the first reference voltage source, the second reference voltage source and the amplification factor, the square wave frequency is determined by the switching frequency of the SPST1ON switch and the SPST1OFF switch, and the SPST1ON switch and the SPST1OFF switch are controlled by the same square wave signal; the alternating current square wave excitation signal is converted into an alternating current signal through a driver, a protection circuit, a cable and a capacitance oil quantity sensor Cx to be tested in sequence.
Further, in step 3, the SPST4ON switch and the SPST4OFF switch are controlled by using square wave signals, so that the current conversion voltage circuit converts the difference value between the alternating current flowing through the capacitance oil quantity sensor Cx to be measured and the current flowing through the reference capacitance C ref into a voltage signal; the SPST2ON switch and the SPST2OFF switch are controlled by using square wave signals, so that the voltage feedback circuit feeds back the filtered voltage signals to the reference capacitor C ref;
in the step 4, the SPST3ON switch is controlled by using a square wave signal, so that the sampling hold and filter circuit samples and filters the signal and outputs a direct-current stable voltage signal V out_p;
The SPST1ON switch, SPST1OFF switch, SPST2ON switch, SPST2OFF switch, SPST3ON switch, SPST4OFF switch are controlled by the same square wave signal, which is generated by the processor control.
The beneficial effects of the invention are as follows:
1. compared with the traditional conditioning method, the invention utilizes the dynamic voltage signal to carry out closed-loop control, fast and stable sampling and holding and filtering circuit and no-load stabilizing circuit, shortens the stabilizing time of the capacitance acquisition conditioning circuit, and can complete the cyclic conditioning acquisition of the capacitance signals of multiple measuring channels; meanwhile, the added no-load stabilizing circuit and the fast stabilizing sample hold and filter circuit do not influence the acquisition precision and the anti-interference capability, are easy to realize, and reduce the multipath capacitance conditioning acquisition cost.
2. The invention uses the no-load stabilizing circuit to realize the stabilizing function of the measured capacitance current when the measuring channel is not selected to be connected by the multiplexer, meanwhile, a diode is added in the sampling hold and filter circuit, the diode and the sampling hold and filter circuit resistor are connected in parallel to form the rapid sampling hold and filter circuit, the current directly flows into the capacitance through the diode in the initial stage, the stabilizing process is accelerated, the current flows into the capacitance through the resistor when the stabilizing process is carried out, and the stabilizing precision of the signal is ensured.
3. The invention uses the dynamic voltage feedback function to realize that the integrated and amplified alternating current dynamic voltage is directly fed back to the reference capacitor C ref, and compared with the feedback acquisition and maintenance circuit voltage feedback, the dynamic voltage feedback measurement channel has smaller time constant, small hysteresis and quicker circuit stability.
4. The front end of the multiplexer is added with the no-load stabilizing circuit, so that an alternating current of the tested capacitor and a ground capacitor of the no-load stabilizing circuit form a current loop, voltage stabilization (alternating current stabilization) at two ends of the ground capacitor is realized, no current loop in the no-load process is avoided, that is, the current flowing through the capacitance oil quantity sensor Cx to be tested is in a stable state before the multiplexer is connected with the measuring channel.
5. Compared with the traditional conditioning method, the square wave signal control using the same frequency and phase for the excitation signal generation and the sensor output signal conditioning utilizes the anti-interference characteristic of modulation and demodulation, and improves the anti-interference capability of capacitance detection.
Drawings
FIG. 1 is a schematic diagram of a dynamic closed-loop control multichannel capacitive oil mass sensor signal conditioning system;
FIG. 2 is a dynamic closed loop control fast settling multi-measurement channel capacitance conditioning circuit;
FIG. 3 is an idle stabilization circuit;
FIG. 4 is a current-switching voltage circuit;
FIG. 5 is a fast stable sample hold and filter circuit;
fig. 6 is an integrating amplifying circuit;
FIG. 7 is a simulation diagram of the fast settling diode start-up time;
Detailed Description
The invention is further illustrated by the following examples in conjunction with the accompanying drawings:
Referring to fig. 1, fig. 2, fig. 3, fig. 4, fig. 5, fig. 6, and fig. 7, fig. 1 is a schematic diagram of a signal conditioning system of a dynamic closed-loop control multi-channel capacitance oil sensor, fig. 2 is a dynamic closed-loop control fast-stability multi-measurement channel capacitance conditioning circuit, fig. 3 is an idle-load stabilizing circuit, fig. 4 is a current-to-voltage circuit, fig. 5 is a fast-stability sample-hold and filter circuit, fig. 6 is an integrating amplifying circuit, and fig. 7 is a fast-stability diode start-up time simulation diagram.
As can be seen from fig. 1, the signal conditioning system of the dynamic closed-loop control multichannel capacitive oil mass sensor of the present embodiment includes an excitation circuit, a driver, a protection circuit, n no-load stabilizing circuits, a multi-measurement channel acquisition controller, a current conversion voltage circuit, an integration amplifying circuit, a sample hold and filter circuit, an a/D acquisition unit, a CPU and a voltage feedback circuit; wherein n is a positive integer greater than or equal to 1;
The excitation circuit, the driver and the protection circuit are electrically connected in sequence; the capacitance oil quantity sensor Cx to be measured is positioned between the protection circuit and the n no-load stabilizing circuits; the n no-load stabilizing circuits, the multi-measurement channel acquisition controller, the current conversion voltage circuit, the integration amplifying circuit, the sampling hold and filtering circuit and the A/D acquisition unit are electrically connected with the CPU in sequence; the input end of the voltage feedback circuit is connected with the output end of the integrating amplifying circuit, and the output end of the voltage feedback circuit is connected with the output end of the multi-measurement-channel acquisition controller.
The excitation circuit is used for outputting alternating current square wave excitation signals with equal positive and negative amplitudes; the duty cycle of the ac square wave excitation signal with equal positive and negative amplitudes in this embodiment may be 50%. The excitation circuit comprises a first reference voltage source, a second reference voltage source, an SPST1ON switch and an SPST1OFF switch; the output end of the first reference voltage source is connected with one end of the SPST1ON switch, the output end of the second reference voltage source is connected with one end of the SPST1OFF switch, and the other ends of the SPST1ON switch and the SPST1OFF switch are connected with the positive input end of the driver; the invention uses the frequency signal to control the SPST1ON and SPST1OFF of the single-pole single-throw switch, realizes the modulation of the direct-current voltage reference signal, and outputs the alternating-current square wave excitation signal; if the frequency output is '1', SPST1ON is conducted, and SPST1OFF is closed; the frequency output "0", SPST1ON is turned OFF and SPST1OFF is turned ON. The driver is used for amplifying the alternating square wave excitation signal; the protection circuit is used for protecting static electricity and lightning and is a conventional circuit; the alternating-current square wave excitation signal is converted into an alternating-current signal through a cable and a capacitance oil quantity sensor Cx to be detected in sequence;
The input ends of the n no-load stabilizing circuits are respectively connected with the output ends of the capacitance oil quantity sensors Cx to be measured of each measuring channel and are used for stabilizing alternating current signals flowing through the capacitance oil quantity sensors Cx to be measured of the measuring channels in no-load state; the empty state measuring channel is an unconnected measuring channel; as shown in fig. 3, one of the no-load stabilizing circuits in the embodiment includes a resistor R1 and a capacitance to ground C1, wherein one end of the resistor R1 is connected to the output end of the measuring channel of the capacitance oil sensor to be measured, and the other end of the resistor R1 is connected to one end of the capacitance to ground C1 and the input end of the multi-measuring channel acquisition controller; the other end of the capacitance to ground C1 is grounded.
The input end of the multi-measurement channel acquisition controller is respectively connected with the output end of each no-load stabilizing circuit and is used for selecting and connecting each measurement channel; the alternating current flowing through the capacitance quantity sensor Cx to be measured is differed from the current flowing through the reference capacitance C ref by negative feedback.
The current conversion voltage circuit is used for converting the difference value between the alternating current flowing through the capacitance oil quantity sensor Cx to be detected and the current flowing through the reference capacitor C ref into a voltage signal; as shown in fig. 4, the current-switching voltage circuit of the present embodiment includes a capacitor C3, a resistor R4, a capacitor C4, SPST4ON and SPST4OFF; one end of a capacitor C3 is connected with the output end of the multi-measurement channel acquisition controller and the output end of the voltage feedback circuit, the other end of the capacitor C3 is connected with one end of a resistor R3 and one end of a resistor R4, the other end of the resistor R3 is connected with one end of an SPST4ON switch, and the other end of the SPST4ON switch is grounded; the other end of the resistor R4 is connected with one end of an SPST4OFF switch, and the other end of the SPST4OFF switch is grounded through a capacitor C4 and is simultaneously connected with the input end of the integrating amplifying circuit.
The integrating amplifying circuit is used for amplifying the voltage signal and outputting amplified alternating current dynamic voltage; the integrating amplifying circuit of this embodiment is shown in fig. 6. The voltage feedback circuit is used for feeding back the amplified alternating current dynamic voltage to the reference capacitor C ref to form a new reference capacitor current value, so that dynamic balance of Cx current of the capacitor oil mass sensor to be detected and reference capacitor current is realized; referring to fig. 1 and 2, the voltage feedback circuit of the present embodiment includes a third reference voltage source, an SPST2ON switch, an SPST2OFF switch and a reference capacitor C ref; one end of the SPST2ON switch is connected with the output end of the integrating amplifying circuit, and the other end of the SPST2ON switch is connected with one end of the reference capacitor C ref; the output end of the third reference voltage source is connected with one end of the SPST2OFF switch, and the other end of the SPST2OFF switch is connected with one end of the reference capacitor C ref; the other end of the reference capacitor C ref is connected with the output end of the multi-measurement channel acquisition controller.
The sampling hold and filter circuit is used for sampling and filtering the alternating current dynamic voltage signal and outputting a direct current stable voltage signal V out_p; as shown in fig. 5, the sample-hold and filter circuit of the present embodiment includes SPST3ON, a resistor R2, a capacitor C2, a follower and two diodes; one end of the SPST3ON is connected with the output end of the integrating amplifying circuit, the other end of the SPST3ON is connected with one end of a resistor R2, the other end of the resistor R2 is grounded through a capacitor C2 and is simultaneously connected with the forward input end of the follower, and the output end of the follower is connected with the reverse input end and the input end of the A/D acquisition unit; two diodes are connected in parallel at two ends of the resistor R2, wherein the anode of one diode is connected with one end of the resistor R2, and the cathode of the other diode is connected with one end of the resistor R2.
The A/D acquisition unit is used for converting V out_p into a digital signal, the CPU is used for acquiring a V out_p digital signal, and the digital signal is converted into a corresponding capacitance oil quantity sensor Cx value to be measured through the following formula:
V out_p= 2×Cx×Vexe_p/ Cref, wherein: v out_p units are V; c x is the capacitance to be measured of the oil quantity sensor, and the unit is pF; v exe_p is the peak voltage of the alternating current excitation signal, and the unit is V; c ref is the reference capacitance in pF.
The method is realized by the following conditioning method:
Step 1: outputting direct current signals with equal amplitude and opposite positive and negative values by using a first reference voltage source and a second reference voltage source; the SPST1ON switch and the SPST1OFF switch are controlled by square wave signals, so that direct current signals with opposite positive and negative are respectively changed into alternating current square wave excitation signals through the SPST1ON switch, the SPST1OFF switch and the driver; the square wave peak voltage V exe_p is determined by the first reference voltage source, the second reference voltage source and the amplification factor, the square wave frequency is determined by the switching frequency of the SPST1ON switch and the SPST1OFF switch, and the SPST1ON switch and the SPST1OFF switch are controlled by the same square wave signal; the alternating current square wave excitation signal is converted into an alternating current signal through a driver, a protection circuit, a cable and a capacitance oil quantity sensor Cx to be tested in sequence.
Step 2: an alternating current signal passing through a capacitance oil quantity sensor Cx to be detected enters an idle load stabilizing circuit;
Step 2.1: when the multi-measurement channel acquisition controller does not select the measurement channel to be connected, an alternating current of the measured capacitor and a ground capacitor of the no-load stabilizing circuit form a current loop, so that voltage stabilization (alternating current stabilization) at two ends of the ground capacitor is realized, no current loop in the no-load process is avoided, namely, before the multi-measurement channel is connected by the multi-selector, the current flowing through the Cx of the capacitance oil quantity sensor to be measured is in a stable state;
Step 2.2: when the multi-path selector selects the measuring channel to be connected, an alternating current signal of the measuring channel corresponding to the capacitance oil quantity sensor Cx to be measured enters a current conversion voltage circuit; the stabilized current flowing through the capacitance oil quantity sensor Cx to be measured enters a new stable state again according to the load change;
Step 3: the SPST4ON switch and the SPST4OFF switch are controlled by using square wave signals, so that an alternating current flowing through a capacitance oil quantity sensor Cx to be detected and a current difference value flowing through a reference capacitor C ref are converted into voltage signals by a current conversion voltage circuit, and the voltage signals are subjected to an integration amplifying circuit to output amplified alternating current dynamic voltage; the amplified alternating current dynamic voltage is fed back to a reference capacitor C ref through a voltage feedback circuit to form a new reference capacitor current value, so that dynamic balance of Cx current of the capacitor oil mass sensor to be detected and reference capacitor current is realized; SPST2ON switch and SPST2OFF in the voltage feedback circuit are controlled by the same square wave signal;
Step 4: the alternating current dynamic voltage output and amplified by the integrating and amplifying circuit passes through a sampling hold and filtering circuit, and the sampling hold and filtering circuit samples and filters signals and outputs a direct current stable voltage signal V out_p; the sample hold voltage is in direct proportion to the measured capacitance; SPST3ON in the sample-and-hold and filter circuit is also controlled by the square wave signal described above;
Step 5: the A/D acquisition unit converts V out_p into a digital signal, the CPU acquires the V out_p digital signal, and the digital signal is converted into a corresponding Cx value of the capacitance oil quantity sensor to be detected through the following formula:
V out_p= 2×Cx×Vexe_p/ Cref, wherein: v out_p units are V; c x is the capacitance to be measured of the oil quantity sensor, and the unit is pF; v exe_p is the peak voltage of the alternating current excitation signal, and the unit is V; c ref is the reference capacitance in pF.
The SPST1ON switch, SPST1OFF switch, SPST2ON switch, SPST2OFF switch, SPST3ON switch, SPST4OFF switch are controlled by the same square wave signal, which is generated by the processor control. The SPSTON, SPSTOFF used in the signal modulation and demodulation process is controlled by a square wave signal with the same duty ratio of 50%, the frequency of the square wave signal is 10KHz, and the frequency range of the square wave signal is generally 5 KHz-30 KHz. This embodiment selects DG413 series SPST analog electronic switches.
Fig. 7 is a simulation result of voltages across the resistor when the fast stable sample-hold and filter circuit has no diode, and the simulation result shows that: after the measuring channel of the multiplexer is connected, larger voltage is applied to two ends of the resistor, the resistor limits the current to rapidly increase, and an RC circuit formed by the resistor and the capacitor has a filtering effect on signals in a stabilizing stage, so that the signal precision is improved. In a word, both the stabilization process is accelerated and the post-stabilization accuracy is ensured.
Claims (8)
1. A dynamic closed-loop control multichannel capacitance oil mass sensor signal conditioning system is characterized in that: the device comprises an excitation circuit, a driver, a protection circuit, n no-load stabilizing circuits, a multi-measurement channel acquisition controller, a current conversion voltage circuit, an integration amplifying circuit, a sampling hold and filtering circuit, an A/D acquisition unit, a CPU and a voltage feedback circuit; wherein n is a positive integer greater than or equal to 1;
The excitation circuit, the driver and the protection circuit are electrically connected in sequence;
the capacitance oil quantity sensor Cx to be measured is positioned between the protection circuit and the n no-load stabilizing circuits;
The n no-load stabilizing circuits, the multi-measurement channel acquisition controller, the current conversion voltage circuit, the integration amplifying circuit, the sampling hold and filtering circuit and the A/D acquisition unit are electrically connected with the CPU in sequence;
The input end of the voltage feedback circuit is connected with the output end of the integrating amplifying circuit, and the output end of the voltage feedback circuit is connected with the output end of the multi-measurement-channel acquisition controller;
The excitation circuit is used for outputting alternating current square wave excitation signals with equal positive and negative amplitudes; the driver is used for amplifying the alternating square wave excitation signal; the protection circuit is used for protecting static electricity and thunder and lightning; the alternating-current square wave excitation signal is converted into an alternating-current signal through a cable and a capacitance oil quantity sensor Cx to be detected in sequence;
The input ends of the n no-load stabilizing circuits are respectively connected with the output ends of the capacitance oil quantity sensors Cx to be measured of each measuring channel and are used for stabilizing alternating current signals flowing through the capacitance oil quantity sensors Cx to be measured of the measuring channels in no-load state; the empty state measuring channel is an unconnected measuring channel;
the input end of the multi-measurement channel acquisition controller is respectively connected with the output end of each no-load stabilizing circuit and is used for selecting and connecting each measurement channel;
making a difference between the alternating current flowing through the capacitance quantity sensor Cx to be detected and the current flowing through the reference capacitor C ref;
The current conversion voltage circuit is used for converting the difference value between the alternating current flowing through the capacitance oil quantity sensor Cx to be detected and the current flowing through the reference capacitor C ref into a voltage signal; the integrating amplifying circuit is used for amplifying the voltage signal and outputting amplified alternating current dynamic voltage; the voltage feedback circuit is used for feeding back the amplified alternating current dynamic voltage to the reference capacitor C ref to form a new reference capacitor current value, so that dynamic balance of the Cx current of the capacitor oil mass sensor to be tested and the reference capacitor current is realized; the sampling hold and filter circuit is used for sampling and filtering the alternating current dynamic voltage signal and outputting a direct current stable voltage signal V out_p; the A/D acquisition unit is used for converting V out_p into a digital signal, the CPU is used for acquiring a V out_p digital signal, and the digital signal is converted into a corresponding capacitance oil quantity sensor Cx value to be measured through the following formula:
V out_p = 2×Cx×Vexe_p / Cref, wherein: v out_p units are V; c x is the capacitance to be measured of the oil quantity sensor, and the unit is pF; v exe_p is the peak voltage of the alternating current excitation signal, and the unit is V; c ref is a reference capacitance in pF;
The no-load stabilizing circuit comprises a resistor R1 and a grounding capacitor C1, one end of the resistor R1 is connected with the output end of a measuring channel of the capacitance oil quantity sensor to be measured, and the other end of the resistor R1 is connected with one end of the grounding capacitor C1 and the input end of the multi-measuring channel acquisition controller; the other end of the grounding capacitor C1 is grounded;
the sample hold and filter circuit comprises SPST3ON, a resistor R2, a capacitor C2, a follower and two diodes;
One end of the SPST3ON is connected with the output end of the integrating amplifying circuit, the other end of the SPST3ON is connected with one end of a resistor R2, the other end of the resistor R2 is grounded through a capacitor C2 and is simultaneously connected with the forward input end of a follower, and the output end of the follower is connected with the reverse input end and the input end of the A/D acquisition unit; two diodes are connected in parallel at two ends of the resistor R2, wherein the anode of one diode is connected with one end of the resistor R2, and the cathode of the other diode is connected with one end of the resistor R2.
2. The dynamic closed-loop control multichannel capacitive oil sensor signal conditioning system of claim 1, characterized by:
The voltage feedback circuit comprises a third reference voltage source, an SPST2ON switch, an SPST2OFF switch and a reference capacitor C ref; one end of the SPST2ON switch is connected with the output end of the integrating amplifying circuit, and the other end of the SPST2ON switch is connected with one end of the reference capacitor C ref; the output end of the third reference voltage source is connected with one end of the SPST2OFF switch, and the other end of the SPST2OFF switch is connected with one end of the reference capacitor C ref; the other end of the reference capacitor C ref is connected with the output end of the multi-measurement channel acquisition controller.
3. The dynamic closed-loop control multichannel capacitive oil sensor signal conditioning system of claim 2, characterized by:
The current conversion voltage circuit comprises a capacitor C3, a resistor R4, a capacitor C4, SPST4ON and SPST4OFF;
One end of the capacitor C3 is connected with the output end of the multi-measurement channel acquisition controller and the output end of the voltage feedback circuit, the other end of the capacitor C3 is connected with one end of the resistor R3 and one end of the resistor R4, the other end of the resistor R3 is connected with one end of the SPST4ON switch, and the other end of the SPST4ON switch is grounded; the other end of the resistor R4 is connected with one end of an SPST4OFF switch, and the other end of the SPST4OFF switch is grounded through a capacitor C4 and is simultaneously connected with the input end of the integrating amplifying circuit.
4. The dynamic closed-loop control multichannel capacitive oil sensor signal conditioning system of claim 3, characterized by:
The excitation circuit comprises a first reference voltage source, a second reference voltage source, an SPST1ON switch and an SPST1OFF switch; the output end of the first reference voltage source is connected with one end of the SPST1ON switch, the output end of the second reference voltage source is connected with one end of the SPST1OFF switch, and the other ends of the SPST1ON switch and the SPST1OFF switch are connected with the positive input end of the driver.
5. The dynamic closed-loop control multichannel capacitive oil sensor signal conditioning system of claim 4, characterized by: the duty cycle of the alternating square wave excitation signal with equal positive and negative amplitude is 50%.
6. A conditioning method based on the dynamic closed-loop control multichannel capacitive oil sensor signal conditioning system of claim 1, characterized by comprising the following steps:
step 1: the processor controls the excitation circuit to output alternating-current square wave excitation signals with equal positive and negative amplitudes, and the alternating-current square wave excitation signals are converted into alternating-current signals through the driver, the protection circuit, the cable and the capacitance oil quantity sensor Cx to be tested in sequence;
Step 2: an alternating current signal passing through a capacitance oil quantity sensor Cx to be detected enters an idle load stabilizing circuit;
step 2.1: when the multi-measurement channel acquisition controller does not select the measurement channel to be connected, alternating current flowing through the capacitance oil quantity sensor Cx to be measured of the measurement channel flows through the no-load stabilizing circuit to be stabilized, so that no current loop in the no-load process is avoided;
Step 2.2: when the multi-path selector selects the measuring channel to be connected, an alternating current signal of the measuring channel corresponding to the capacitance oil quantity sensor Cx to be measured enters a current conversion voltage circuit;
Step 3: the current conversion voltage circuit converts the difference value between the alternating current flowing through the capacitance oil quantity sensor Cx to be detected and the current flowing through the reference capacitor C ref into a voltage signal, and the voltage signal passes through the integrating and amplifying circuit to output amplified alternating current dynamic voltage; the amplified alternating current dynamic voltage is fed back to a reference capacitor C ref through a voltage feedback circuit to form a new reference capacitor current value, so that dynamic balance of Cx current of the capacitor oil mass sensor to be detected and reference capacitor current is realized;
Step 4: the alternating current dynamic voltage output and amplified by the integrating and amplifying circuit passes through a sampling hold and filtering circuit, and the sampling hold and filtering circuit samples and filters signals and outputs a direct current stable voltage signal V out_p;
Step 5: the A/D acquisition unit converts V out_p into a digital signal, the CPU acquires the V out_p digital signal, and the digital signal is converted into a corresponding Cx value of the capacitance oil quantity sensor to be detected through the following formula:
v out_p = 2×Cx×Vexe_p / Cref, wherein: v out_p units are V; c x is the capacitance to be measured of the oil quantity sensor, and the unit is pF; v exe_p is the peak voltage of the alternating current excitation signal, and the unit is V; c ref is the reference capacitance in pF.
7. The conditioning method according to claim 6, wherein step 1 is specifically: outputting direct current signals with equal amplitude and opposite positive and negative values by using a first reference voltage source and a second reference voltage source; the SPST1ON switch and the SPST1OFF switch are controlled by square wave signals, so that direct current signals with opposite positive and negative are respectively changed into alternating current square wave excitation signals through the SPST1ON switch, the SPST1OFF switch and the driver; the square wave peak voltage V exe_p is determined by the first reference voltage source, the second reference voltage source and the amplification factor, the square wave frequency is determined by the switching frequency of the SPST1ON switch and the SPST1OFF switch, and the SPST1ON switch and the SPST1OFF switch are controlled by the same square wave signal; the alternating current square wave excitation signal is converted into an alternating current signal through a driver, a protection circuit, a cable and a capacitance oil quantity sensor Cx to be tested in sequence.
8. The conditioning method according to claim 7, characterized in that: in the step 3, the SPST4ON switch and the SPST4OFF switch are controlled by using square wave signals, so that the current conversion voltage circuit converts the difference value between the alternating current flowing through the capacitance oil quantity sensor Cx to be detected and the current flowing through the reference capacitor C ref into a voltage signal;
the SPST2ON switch and the SPST2OFF switch are controlled by using square wave signals, so that the voltage feedback circuit feeds back the filtered voltage signals to the reference capacitor C ref;
in the step 4, the SPST3ON switch is controlled by using a square wave signal, so that the sampling hold and filter circuit samples and filters the signal and outputs a direct-current stable voltage signal V out_p;
the SPST1ON switch, SPST1OFF switch, SPST2ON switch, SPST2OFF switch, SPST3ON switch, SPST4OFF switch are controlled by the same square wave signal, which is generated by the processor control.
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| JPH10221155A (en) * | 1996-12-06 | 1998-08-21 | Omron Corp | Weight-detecting apparatus and oil amount sensor using the same |
| CN204388965U (en) * | 2014-11-11 | 2015-06-10 | 深圳市南航电子工业有限公司 | A kind of capacitance-type fuel quantity survey sensor and system utilizing digital data transmission |
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